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This paper describes how a 3D-Audio system for use in fighter aircrafts was evaluated in an experiment, by comparing localization performance between real and virtual sound sources. Virtual sound sources from 58 selected directions were evaluated, while 16 of these directions were also evaluated using real sound sources, i.e. loudspeakers. 13 pilots from the Royal Danish Air Force and 13 civil persons were used in the test. The localization performance was split into a constant and a stochastic difference between the perceived direction and the desired direction (stimulus). The constant difference is a localization offset and the stochastic difference is a measure for the localization uncertainty. Stimuli length of both 250 ms and 2's enabled investigation of the importance of head movements, i.e. using head tracking. Real and virtual sound sources could be located with an uncertainty of 10o and 14o degrees for azimuth while the uncertainty for elevation was 12o and 24o (real and virtual sound sources). No significant localization offset was found for azimuth, while an average offset for elevation of 3o 6o degrees was found using long stimuli. A significant difference between the localization offset obtained in different directions was found especially for elevation, where the offset was found to have a strong correlation to the stimuli elevation.